Physiology Of Balance

Question 1

What is the vestibular system & where is it located

Answer 1

Sensory apparatus of balance located in the inner ear

Question 2

What are the five key end organs of the vestibular system

Answer 2

The two otolith organs (urticaria & saccule)
The three semicircular canals

Question 3

What structure(s) are involved in sensing head position (linear movement)

Answer 3

The otolith organs - urticle & saccule

Question 4

Where are the otolith organs located

Answer 4

In the vestibule

Question 5

What otolith organ detects horizontal movement of the head

Answer 5

Urticle

Question 6

What otolith organ detects vertical movement of the head

Answer 6

saccule

Question 7

What is the sensing organs of the otolith organs called

Answer 7

The macule

Question 8

What does the macule of otolith organs contain

Answer 8

Stereocilia & their supporting hair cells
Gelatinous matrix with otoconia

Question 9

What are otoconia

Answer 9

‘Ear stones’

Question 10

Kinocilium vs stereocilia

Answer 10

Kinocilium - the largest hair-like projection on hair cells that serves as a reference for stereocilia movement

Stereocilia - all other hair-like projections that move on the hair cells and cause release of neurotransmitters

Question 11

What would increase the rate of action potential firing from the hair cells

Answer 11

Deflection of stereocilia towards the Kinocilium

Question 12

What would decrease the rate of action potential firing from the hair cells

Answer 12

Deflection of stereocilia away from the Kinocilium

Question 13

How are the macula’s of the saccule & utricle located with respect to each other & why is this important

Answer 13

They are oriented 90 degrees to one another so that they respond to positions in different planes

Question 14

Describe the steps that initiate an action potential in the vestibular nerve as a result of linear head movement

Answer 14

• When the head moves, gravity causes the stones in the membrane of the macula to move
• The movement of the stones causes stereocilia to bend
• This initiates an action potential in the vestibular nerve fibers

Question 15

What end organs of the vestibular system detect head movement

Answer 15

semicircular canals

Question 16

What are the three semicircular canals

Answer 16

Anterior
Lateral
Posterior

(Two in horizontal plane, one in vertical plane)
(90 degree orientation)

Question 17

What is the name of the region at the base of the semicircular canal where it meets the vestibule

Answer 17

Ampulla

Question 18

What does the ampulla contain

Answer 18

Crista ampullaris (cupula, hair cells & sensory nerve fibres)

Question 19

How does head movement lead to CN VIII firing

Answer 19

Deflection of the stereocilia caused by motion of the endolymph in the semi circular canal

This results in an opening (or closing) of the transduction channels of hair cells

This changes the membrane potential of the hair cells resulting in release of neurotransmitters & CNVIII firing

Question 20

What part of the vestibular system is responsible for sensing head position

Answer 20

The otolith organs (urticle & saccule) in the vestibule

Question 21

What otolith organ senses horizontal movement

Answer 21

Urticle

Question 22

What otolith organ senses vertical movement

Answer 22

Saccule

Question 23

What is the name of the sense organ of each otolith organ

Answer 23

Macula

Question 24

What is found in the macula

Answer 24

Stereocilia that project upwards into the gelatinous matrix with otocania

Question 25

Kinocilium vs sterocilia

Answer 25

Kinocilium is the largest hair-like projection on hair cells that serves as a reference point for the surrounding sterocilia

Question 26

What would increase the action potential firing rate of the hair cells

Answer 26

deflection of stereocilia towards the kinocilium

Question 27

What would decrease the action potential firing rate of the hair cells

Answer 27

deflection of stereocilia away from the kinocilium

Question 28

Vestibule-ocular reflex vs nystagmus

Answer 28

Vestibule-ocular reflex - Reflex that helps stabilise vision during head movements by automatically adjusting eyes to counteract head movement. Is a physiological nystagmus Nystagmus - Involuntary eye movement. Can be physiological (VOR) or pathological.

Question 29

What would happen to the firing rate of the left & right horizontal (aka lateral) semicircular canals if you were to turn your head to the left

Answer 29

Excitation on left hand side, Inhibition on right hand side

Question 30

What would happen to firing rate of the left & right horizontal (aka lateral) semicircular canals if you were to turn your head to the right

Answer 30

Inhibition on left hand side, Excitation on right hand side

Question 31

What would happen in right vestibular damage

Answer 31

The right semicircular canal is not working/ firing ⇒ The left hand side is firing more than the right ⇒ The brain perceives this as turning left ⇒ Vertigo & nystagmus => This is similar for left vestibular damage

Question 32

What movements are detected by the three different semicircular canals

Answer 32

Left & right rotation ⇒ lateral (horizontal) semicircular Right & left lateral flexion ⇒ posterior semicircular canals Flexion & extension ⇒ anterior semicircular canal

Question 33

What are the three central pathways of vestibular nuclei

Answer 33

- Vestibulospinal tract - motor output to neck, back and leg muscles - Medial longitudinal fasciculus & ocular muscles - eye motor output - Medial lemniscus and thalamus to cerebrum